JPH0295708A - Valve closing device for four-cycle engine - Google Patents

Abstract

PURPOSE:To set both closing/opening timing and a lift of each valve at the most suitable value by rotating a rocker shaft by a predetermined angle so as to freely select one cam-profile out of the two kinds prepared for a cam which operates the valve in correspondence to each engine speed range. CONSTITUTION:When a rocker shaft 7 is rotated by a predetermined angle at a medium or high engine speed range by a servo motor or the like in an operational state in which the first rocker arm 5 touches the peripheral surface of a low-speed revolution cam 2 and in which valve stems 8 and 9 move up and down in conformity with a cam profile of the low-speed revolution cam 2, a surface 11b of an eccentric bush 11, which is most away from the shaft center of the rocker shaft 7, is situated at the topmost position, while only a supporting part 'a' of the second rocker arm 6 moves up to the position equivalent to that of a supporting part 5a of the first rocker arm 5. Then the peripheral surface of a high-speed revolution cam 3 fixed to a cam shaft 4 is brought into contact with the second rocker arm 6, while valve stems 8 and 9 move up and down in conformity with the cam profile of the high-speed revolution cam 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a valve train for driving intake and exhaust valves of a four-stroke engine.

[Conventional technology]

Generally, in a four-stroke engine installed in vehicles such as automobiles and motorcycles, intake and exhaust valves are arranged above the combustion chamber, and the valve train is equipped with a camshaft to operate the intake and exhaust valves. There is. When this camshaft is rotated by the power of the engine, the intake and exhaust valves move up and down at a predetermined timing by a cam with a unique cam profile formed on the camshaft, sucking in the air-fuel mixture and exhausting combustion scum. .

Note that in the conventional valve train described above, each of the intake and exhaust valves is always operated by a cam with the same cam profile, so the opening and closing of each valve is set according to the engine speed. The lift amount of the valve, which is moved up and down by the timing and rotation of the cam, remains constant without fluctuation.

[Problem to be solved by the invention]

By the way, the above-mentioned 4 devices installed in vehicles such as motorcycles
Cycle engines are required to achieve high output within a wide rotation speed range from low rotation speeds to medium and high rotation speed regions, that is, to obtain a wide power band.

However, in the conventional valve train described above, each of the intake and exhaust valves is always operated by a cam having the same cam profile, so the opening/closing timing of each valve and the lift amount of the valve are always constant without fluctuation. Therefore, the output characteristics of the engine are generally limited by the cam profile of the cam that operates the valve, and the output characteristics have a peak value in a specific engine speed range. It was not possible to obtain even higher output over a wide rotation speed range.

In view of the above-mentioned circumstances, it is an object of the present invention to provide a valve train for a four-stroke engine that improves output within a wide rotation speed range from a low rotation speed range to a medium/high rotation speed range.

[Means to solve the problem]

In order to achieve the above-mentioned problems, the present invention provides a cam 10.
A camshaft in which two types of cams with different eels are formed adjacent to each other, and the cam lift amount of at least one of the cams is larger than the cam lift amount of the other cam;
A first rocker arm that is disposed below a cam with a small cam lift amount among the cams formed on the camshaft and directly contacts a valve head that opens and closes a combustion chamber, and a cam formed on the camshaft. a second rocker arm that is disposed below the cam with a large cam lift amount and that engages with the upper surface of the first rocker arm;
It is rotatably supported, and is fitted into each of the support parts of the first and second rocker arms, and the part that is fitted into the support part of the second rocker arm has a larger diameter than other parts. , and a rocker shaft in which an eccentric large-diameter portion is formed whose axis is eccentric from the axis of other parts, and by rotating the rocker shaft by a predetermined angle in a low rotational speed range of the engine, the rocker shaft is The eccentric large diameter portion moves the support portion of the second rocker arm downward relative to the support portion of the first rocker arm, thereby forming a cam formed on the camshaft with a large cam lift amount. and the second rocker arm, the cam with the small cam lift amount is brought into contact with the first rocker arm, and the valve is made to follow the cam profile of the cam with the small cam lift amount. Along with operating the
By rotating the rocker shaft by a predetermined angle in a medium/high rotation speed range, the eccentric large diameter portion raises the support portion of the second rocker arm to a position equivalent to the support portion of the first rocker arm. As a result, the cam with a small cam lift amount is released from contact with the first rocker arm, the cam with a large cam lift amount is brought into contact with the second rocker arm, and the valve is moved into contact with the cam with a large cam lift amount. It operates by following the cam profile of the cam.

[Effect]

According to the above-mentioned valve train, the cam profile of the cam that operates the valves can be selected from two types according to each rotation range of the engine, so the opening/closing timing of each valve and the lift amount of the valve can be adjusted depending on the engine rotation. It can be set to the optimal value depending on the number range.

〔Example〕

Hereinafter, one embodiment of a valve train according to the present invention will be described in detail.

FIG. 1 is a conceptual perspective view of essential parts showing a valve train 1 according to the present invention. The valve operating device 1 is provided at two locations per cylinder, one on the intake valve side and one on the exhaust valve side.

This valve train 1 includes a camshaft 4 in which two types of cams 2.3 having different cam profiles are formed adjacent to each other, and first and second rocker arms 5.6 disposed below the camshaft 4. and a rocker shaft 7 which is fitted into each support portion 5a, 6a of each rocker arm 5.6 and rotatably supported by a bearing portion (not shown).

Among these, the cam 2 formed on the camshaft 4 has a cam profile suitable for improving engine output in the so-called low-speed rotation range, where the cam lift amount is small and the valve opening/closing period is set short. On the other hand, the cam 3 formed adjacent to the cam 2 has a larger cam lift and a longer valve opening/closing period than the cam 2 over the entire circumference, and is symmetrical to the cam 2. In addition, it is a cam (hereinafter referred to as a high-speed rotation cam) that has a cam profile suitable for improving the output of the engine at so-called medium and high speed rotations.

on the other hand. Of the first and second rocker arms 5.6, the first rocker arm 5 is disposed below the low-speed rotation cam 2 formed on the camshaft 4, and its tips 15b and 5c are bifurcated. , are arranged so as to directly contact the heads of valve stems 8 and 9 of valves that open and close combustion chambers of an engine (not shown). Also, the adjacent second rocker arm 6
is disposed below the high-speed rotation cam 3 formed on the camshaft 4, and the tip 6b is connected to the first rocker arm 5.
It is disposed so as to engage with the top surface 5d of the tip.

On the other hand, the rocker shaft 7 that rotatably supports the first and second rocker arms 5.6 described above has a diameter larger than that of the pond part of the rocker shaft 7, and the axis of the rocker shaft 7 is larger than that of the other parts. An eccentric large diameter portion 10 is formed eccentrically from the axis, and this eccentric large diameter portion 10 is fitted into the support portion 6a of the second rocker arm 6. And this eccentric large diameter part 10
is composed of an eccentric bush 11 fitted into the lower car shaft 7 and a pin 12 that fixes the eccentric bush 11 to the rocker shaft 7. In addition, the second
As shown in the figure, the dimensional tolerance of the eccentric bush 11 and the rocker shaft 7 is closely controlled fF1, and the holes 11a and 7 have a diameter slightly smaller than the diameter of the bottle 12.
A is formed in the eccentric bush 1 by driving the pin 12 into the holes 11a and 7a.
1 and the rocker shaft 7 are fixed to each other.

In FIG. 1, reference numeral 13 indicates a threaded portion for adjusting valve clearance, and reference numeral 14 indicates a valve spring.

Next, the operation of the above-mentioned valve train 1 will be explained, and the configuration will also be explained in more detail.

When the rocker shaft 7 is rotated by a predetermined angle in the low rotational speed range of a four-cycle engine by a rotating means such as a servo motor or a rack and pinion (not shown) and stopped at the position shown in FIG. Surface 1 of the eccentric bush 11 furthest from the axis
1b is located at the lowest end, only the support portion 6a of the second rocker arm 6 moves downward relative to the support portion 5a of the first rocker arm 5 and stops there.

According to such a stop position of the rocker shaft 7, only the support part 6a of the second rocker arm 6 moves downward relative to the support part 5a of the first rocker arm 5, so that the position shown in FIG. As shown in Figure 3, which is a sectional view of the main part,
A gap t is formed between the circumferential surface of the high-speed rotation cam 3 formed on the camshaft 4 and the second rocker arm 6, so that the high-speed rotation cam 3 and the second rocker arm 6 is released from contact with the peripheral surface, and the high-speed rotation cam 3 rotates in an idle state.

It goes without saying that the outer diameter and eccentricity of the eccentric bush 11 are set to form the above-mentioned gap t.

On the other hand, according to the stop position of the rocker shaft 7 shown in FIG. The first rocker arm 5 and the circumferential surface of the low-speed rotation cam 2 are always in contact with each other, so that when the camshaft 4 rotates at the stop position of the rocker shaft 7 shown in FIG. The stems 8 and 9 are the cams 2 for low speed rotation.
Since the valve moves up and down following the cam profile, the combustion chamber can be opened and closed at low speed while ensuring suitable valve opening/closing timing and valve lift amount.

On the other hand, the rocker shaft 7 is rotated by a predetermined angle from the position shown in FIG. 1 in the middle/high speed range of the four-cycle engine by the above-mentioned rotation means such as a servo motor (not shown), and the same portion as shown in FIG. When the eccentric bushing 11 is stopped at the position shown in FIG. Only the support portion 5 of the first rocker arm 5
It rises to the same position as a and stops there.

According to such a stop position of the rocker shaft 7, only the support portion 6a of the second rocker arm 6 moves upward relative to the support portion 5a of the first rocker arm 5, so that the position shown in FIG. As shown in FIG. 5, which is a side sectional view of a main part, the circumferential surface of the high-speed rotation cam 3 formed on the camshaft 4 comes into contact with the second rocker arm 6.

On the other hand, when the peripheral surface of the high-speed rotation cam 3 formed on the camshaft 4 shown in FIG. 4 comes into contact with the second rocker arm 6, the high-speed rotation cam 3 becomes the low-speed rotation cam 2, and the tip 6 of the second rocker arm 6 is
b is disposed so as to engage with the upper end surface 5d of the first rocker arm 5, so that when the camshaft 4 rotates at the stop position of the rocker shaft 7 shown in FIG. The cam 2 rotates in an idle state, and the first rocker arm 5 rotates with the second rocker arm 6.
The valve stem 8.9 of the valve that opens and closes the combustion chamber moves up and down following the cam profile of the high-speed rotation cam 3, so that the valve can rotate at high speed. The combustion chamber is opened and closed while ensuring suitable valve opening/closing timing and valve lift amount.

Note that when the high-speed rotation cam 3 shown in FIG. 3 is not operating, the second rocker arm 6 is not restrained in any way, so the rocker shaft 7 is connected to the tip 15d of the first rocker arm 5 that moves up and down. There is a risk that it may become a source of noise due to factors such as a collision, but in such a case, the third
As shown in FIG. 6, where the same parts as in the figure are designated by the same reference numerals, the tip 6b of the second rocker arm 6 and the first rocker arm 5
When the coil spring 20 is interposed between the tip i5d and the two are connected to each other, the second rocker arm 6 moves up and down in synchronization with the movement of the first rocker arm 5. It is possible to eliminate fraying of the rocker arm 6 of No. 2.

In addition, in order to eliminate fraying of the second rocker arm 6 when the high-speed rotation cam 3 is not operating, the tip 21a is fixed as shown in the conceptual perspective view of FIG.

A coil spring 21 in which 21b is bent in opposite directions is used, and this coil spring 21 is connected to a first rocker arm 5 and a second rocker arm as shown in FIG. 8, in which the same parts as in FIG. 6, and the first and second rocker arms 5 and 6 are sandwiched between their tip portions 21a and 2fb, so that the movement of the first rocker arm 5 causes the second rocker arm 6 to move.
The movements of the two may be synchronized.

In the above embodiment, in constructing the eccentric large-diameter portion 10, as shown in FIG. Although the eccentric bush 11 and the rocker shaft 7 are fixed by being driven in and press-fitted, the present invention is not limited to the above embodiment, and the same parts as in FIG. 2 are indicated by the same reference numerals. As shown in FIG. 9, the recesses 11a and 7a formed in the eccentric bush 11 and the rocker shaft 7 are formed into so-called stupid holes with loose dimensional tolerances.

After the pin 12 is slidably inserted into the pin 7a, the entire eccentric push 11 is inserted into the support portion 6a of the second rocker arm 6, and the rocker shaft 7 is rotatably supported. A coiled thrust spring 32 is disposed on the rocker shaft 7 on the side of one of the bearing parts 30 and 31, and the urging force of the thrust spring 32 causes the entire first and second rocker arms 5 and 6 to be rotated. Bearing part 3o on the side (second rocker arm 6fJI!l)
It is also possible to position the pin 12 by pressing it to the side, thereby preventing the pin 12 from coming off on the inner circumferential wall of the support portion 6a of the second rocker arm 6, and also connecting the eccentric shaft 11 and the rocker shaft 7.

Incidentally, as in the embodiment shown in FIG.
A, 7a are formed into so-called stupid holes whose dimensional tolerances are loosely controlled, and this hole 11a.

After the pin 12 is slidably inserted into the pin 7a, the entire eccentric push 11 is inserted into the support part 6a of the second rocker arm 6, and further positioned by the thrust spring 32, and the support part If the inner circumferential wall 6a is configured to prevent the pin 12 from slipping out, the valve train 1 can be easily moved by expanding and contracting the thrust spring 32.
Assembling and disassembling work will be carried out, and there will also be a
1a.

Since 7a may be a so-called dumb hole with loose dimensional tolerance control, the dimensional tolerance can be easily controlled and the manufacturing process of the valve train is further simplified.

In each of the above embodiments, the valve train 1 according to the present invention is applied to a so-called 4-valve engine having two valves on the intake and exhaust sides, but the present invention is applicable to the above embodiments. Without limitation, the valve operating device 1 according to the present invention may be applied to the intake and exhaust sides of a so-called two-valve engine having one valve each on the intake and exhaust sides.

Further, in the above embodiment, the eccentric large diameter portion 10 was constituted by the eccentric bush 11 and the pin I2, but the present invention is not limited to the above embodiment.
The eccentric large diameter portion 10 may be formed integrally with the rocker shaft 7. [Effects of the Invention] As explained above, in the valve train of the present invention, the cam profile of the cam that operates the valve according to each rotation range of the engine is selected from two types according to the engine rotation speed, and each Since the valve opening/closing timing and valve lift amount can be changed to the optimal values according to the engine speed range, the 4-stroke engine can be operated within a wide speed range from low speeds to medium and high speeds. In addition, in the valve train of the present invention, since the rotational motion of the rocker shaft at the time of cam selection is converted into the vertical motion of the second rocker arm by the eccentric large diameter portion, No major stress is applied to each part during selection, so cam selection is performed smoothly.

Furthermore, since the valve train of the present invention is constructed without making any major changes to conventional valve trains, it can be installed on a conventionally shaped cylinder head with minimal processing. Therefore, when implementing the present invention, there is also the advantageous effect that the increase in production costs can be suppressed to the minimum limit.

[Brief explanation of the drawing]

1st (2I is a conceptual perspective view of a valve train according to the present invention,
Fig. 2 is a cutaway plan view of the main part of Fig. 1, Fig. 3 is a side sectional view of the main part of Fig. 1, Fig. 4 is a conceptual perspective view showing the operation of the valve train according to the present invention, and Fig. 5. is a sectional side view of the main part of FIG. 4, FIG. 6 is a sectional side view of the main part showing a spring connecting the first and second rocker arms, and FIG. 7 is a sectional side view of the main part of the spring connecting the first and second rocker arms. FIG. 8 is a conceptual perspective view showing another embodiment of the springs to be connected, FIG. 8 is a fragmentary plan view of the main parts showing the state in which the spring shown in FIG. 7 is installed, and FIG. FIG. 2 is a fragmentary plan view of a main part showing an example. DESCRIPTION OF SYMBOLS 1... Valve train, 2.3... Cam, 4... Camshaft, 5... First rocker arm, 6... Second
rocker arm, 5a, 6a... support part, 7...
Rocker shaft, 8.9... Valve (valve stem), 10... Eccentric large diameter section, 11... Eccentric bush, 12... Pin. Figure 2 Figure 5\ Figure 6 b ゝ), 1b Figure 7 Figure 8

Claims (2)

[Claims] (1) A camshaft in which two types of cams with different cam profiles are formed adjacent to each other, and the cam lift amount of one cam is larger than the cam lift amount of the other cam; A first rocker arm is disposed below the cam with a small cam lift and directly contacts the valve head that opens and closes the combustion chamber, and a first rocker arm is disposed below the cam with a large cam lift among the cams formed on the camshaft. a second rocker arm that is disposed on and engages with the upper surface of the first rocker arm; At the same time, an eccentric large-diameter portion is formed in a portion of the second rocker arm that is fitted into the support portion, the diameter being larger than that of other portions, and the axis of which is eccentric from the axis of the other portions. a shaft, and by rotating the rocker shaft by a predetermined angle, the eccentric large diameter portion moves the supporting portion of the second rocker arm downward relative to the supporting portion of the first rocker arm. the cam with the large cam lift amount is released from contact with the second rocker arm, the cam with the small cam lift amount is brought into contact with the first rocker arm, and the valve is moved into the cam with the small cam lift amount. By operating the cam by following the cam profile of the cam and rotating the rocker shaft by a predetermined angle, the eccentric large diameter portion makes the supporting portion of the second rocker arm equal to the supporting portion of the first rocker arm. the cam with a small cam lift amount is released from contact with the first rocker arm, the cam with a large cam lift amount is brought into contact with the second rocker arm, and the valve is raised to the above-mentioned position. A valve train for a four-stroke engine, characterized in that the valve train operates by following the cam profile of a cam with a large cam lift. (2) In the valve train according to claim (1), the eccentric large-diameter portion includes an eccentric bushing that is pivotally supported by the rocker shaft and that is fitted into a support portion of the second rocker arm; When the bushing and the rocker shaft are slidably inserted into holes formed respectively, and inserted into the support portion of the second rocker arm, the inner circumferential wall of the support portion of the second rocker arm prevents the movement of the bush. The rocker shaft has a thrust spring that simultaneously urges and positions the first rocker arm and the second rocker arm toward the second rocker arm. Valve gear for a 4-stroke engine.